Bioelectrical impedance analysis (BIA) is a noninvasive, safe, inexpensive and portable technique for rapid assessment of body composition and body water that requires minimal patient collaboration. BIA measures the voltage and phase angle of a signal generated by injecting a small sinusoidal electrical current at a single or multiple frequencies into the body, typically from hand to foot and computes the complex impedance values, with the real part of the impedance representing resistance (R) and the imaginary part of the impedance representing the reactance (Xc).
Multi-frequency analysis is used to determine the amount of extracellular (ECW) and intracellular water (ICW) based on a simple model of a purely capacitive membrane separating a resistive intra and extracellular space. Therefore ECW can be estimated from the impedance at low frequency and total body water (TBW) from the real component of the impedance at high frequency where the capacitive effect of the cell membrane can be neglected. ICW can be calculated from the difference between TBW and ECW.
In contrast to BIA, bioelectrical impedance vector analysis (BIVA) does not require any assumption about body geometry, electrical tissue models or regression analysis. In the BIVA representation body composition is described as a vector with resistance (R) as the abscissa, and reactance (Xc) as the ordinate normalized by the subject's height (H). To achieve a wider use of BIA/BIVA applications and to promote the use of BIA technology by patients and health care providers with limited training, it is desired to have a portable, low cost, battery operated and durable multi-frequency impedance spectrometer.